A fire hydrant delivers water of density ρ at a volume rate l. The water travels vertically upwards through the hydrant and then does 900 turn to emerge horizontally at speed υ. The pipe and nozzle have uniform cross-section throughout. The force exerted by water on the corner of the hydrant is
√2ρvl
In time Δt, momentum of water entering the hydrant
P1=(ρLΔt)v^j
Momentum of water while leaving the hydrant in time Δt is
P2=(ρLΔt)v(−^i)
Change in momentum in time Δt is
ΔP=P2−P1=ρLt(−^i−^j)
|ΔP|=ρLΔtv√(−1)2+(−1)2
=√2ρLΔtv
Force exerted by water,F=F=|ΔP|Δt=√2ρLv